Exhaust gas treatment device

ABSTRACT

An exhaust gas treatment device, in particular for an internal combustion engine, is fitted with a housing including an entrance and an exit. At least one porous substrate is accommodated in the housing and has an exhaust gas flowing through the substrate. The porous substrate is arranged in the flow path from the entrance to the exit. At least one thermoelectric generator is provided on the housing.

RELATED APPLICATION

This application claims priority to DE Application No. 10 2008 063861.7, which was filed Dec. 19, 2008.

FIELD OF THE INVENTION

The present invention relates to an exhaust gas treatment device, inparticular for an internal combustion engine of a vehicle.

BACKGROUND OF THE INVENTION

For the treatment, more particularly for the purification of exhaustgases of internal combustion engines, e.g., diesel engines of passengerautomobiles, it is known to arrange porous, gas-permeable substrates ina closed metallic housing in an exhaust pipe so that the exhaust gasflows through the substrate.

Exhaust gas treatment devices of this type, which may involve, forexample, diesel particulate filters or catalytic converters, such as,e.g., for NO_(x) reduction, are inserted in the exhaust pipe in such away that all of the exhaust gas has to flow through the exhaust gastreatment device. In the process, the exhaust gas is forced to passthrough the porous substrate which has a filter effect and/or effects acatalytically activated chemical reaction with a chemically activecoating. An exhaust gas treatment occurs here, e.g., by chemicalconversion, by mechanical deposition of particles carried along with theexhaust gas, e.g., soot particles, in the pores of the substrate, or acombination of different methods.

It is known to bring the substrate into the shape of a hollow bodyhaving one or more walls. The hollow body is arranged in the housingsuch that the exhaust gas must always flow through at least one wall ofthe hollow body to pass from an entrance of the housing to an exitthereof.

The exhaust gas stream that flows through the housing has a temperatureof several hundred degrees Celsius.

It is the object of the invention to utilize the thermal energy of theexhaust gas stream.

SUMMARY OF THE INVENTION

The exhaust gas treatment device, which in particular is provided for aninternal combustion engine, includes a housing with an entrance and anexit. At least one porous substrate is accommodated in the housing andhas an exhaust gas flowing through the substrate. The substrate isarranged in a flow path from the entrance to the exit. Further, at leastone thermoelectric generator is arranged on the housing. Thermoelectricgenerators are devices for converting thermal energy into electricalenergy. They include thermocouple elements which operate on theso-called “Seebeck effect” and in which a thermoelectric voltage isgenerated based on the specific pairing of materials used and thetemperature difference prevailing across the thermocouple element. Inthis way, the thermal energy of the exhaust gas stream can be utilizedto generate electrical energy. In addition, a cooling effect on thehousing is produced, which results in, e.g., a reduction in thedifferences in the thermal expansion between the housing and thesubstrate.

The thermoelectric generators employed may be known conventionalthermoelectric generators.

The thermoelectric generator is preferably applied on an outside of thehousing to be able to utilize a major part of the thermal energy givenoff by the exhaust gas stream to the housing. Thermoelectric generatorsare advantageously used in the form of sheets or strips and arepreferably so flexible that they can be well adjusted to the surface ofthe housing. It is possible to cover essentially the entire outersurface of the housing with one or more thermoelectric generators.

The thermoelectric generators may be fastened to the housing in anysuitable manner, such as, e.g., by soldering or brazing, it being ofadvantage here if a direct, large-area connection having good thermalconductivity exists between the thermoelectric generator and the outersurface of the housing.

Exhaust gas treatment devices in which the exhaust gas flows directlyagainst an inner wall of the housing are advantageous to theconfiguration because a direct heat transfer from the exhaust gas to thehousing, and thus a high yield of thermal energy, is ensured. Thehousing is designed, for example, in the form of a cylinder havingconnecting funnels applied at the entrance and at the exit. Thecylindrical section has a larger diameter than an adjacent exhaust gaspipe. The inner wall is preferably the inner side of the cylindricalperipheral wall, which can be provided with a known, e.g. catalyticallyactive, coating which has such a small thickness that it is normally ofno consequence with regard to the heat conduction.

In one example, the substrates through which the exhaust gas flows aresupported in the housing without the interposition of a support mat, asa result of which the housing is uninsulated from the inside.

Possible geometries to be used for the hollow body include, e.g., a pairof cone envelopes or truncated cone envelopes fitted inversely into eachother, four- or multi-sided pyramid envelopes or truncated pyramidenvelopes, or a pair of cylinder envelopes arranged concentrically inrelation to each other.

Such envelopes may be simply produced by reshaped sheets.

In one example, the substrate consists of a metal foam, metal spongeand/or a metallic hollow sphere structure, or a wire mesh or wire knit.In contrast to ceramic substrates, which are wrapped in an elasticsupport mat and are accommodated in the housing, in the case of a bodymade of a porous metal substrate, in particular a hollow body, no suchthermally insulating material is arranged on the inner wall of thehousing, so that a high yield of thermal energy is ensured. In contrastto ceramic substrates, this special metal substrate has an inherentelasticity which allows a press fit in the housing, in particularwithout additional fastening means.

In another known form, the substrate consists of one or more porousceramic blocks.

The difference in temperature necessary for operation of thethermoelectric generator or generators is implemented in a radialdirection from an interior of the housing to the outside.

To increase the difference in temperature, heat conducting fins may beprovided on the inside and/or on the outside of the exhaust gastreatment device, which preferably project radially from the housing.Inside fins serve to withdraw as much heat as possible from the exhaustgas stream to provide as high a temperature as possible on the radiallyinner side of the thermoelectric generator, whereas outside fins,preferably on the thermoelectric generator, serve to radiate as muchheat as possible from the radially outer side of the thermoelectricgenerator to cause the temperature there to be as low as possible.

The difference in temperature may be further increased by makingprovision for a cooling device for the thermoelectric generator.

The cooling device may consist of a cooling body, for example, withcooling fins formed thereon, for instance, the cooling body being placedon the outside of the thermoelectric generator or generators.

In one example, the cooling device surrounds the thermoelectricgenerator on the outside to dissipate heat to the surroundings of theexhaust gas treatment device.

The cooling device may include at least one cooling duct having acooling medium flowing through the cooling duct. The cooling duct orducts is/are preferably formed between the thermoelectric generator anda wall of the cooling device and may extend in a longitudinal directionof the exhaust gas treatment device.

It is also possible to employ a cooling liquid. In this configuration,the cooling device may be connected to a conventionally provided coolingcircuit of the internal combustion engine, for example.

It is, however, of advantage to use air as the cooling medium since inthis way the weight of the exhaust gas treatment device may be reducedand the device may have a simpler structure.

The cooling device includes, for example, at least one inlet having asupply opening. Air from the surroundings of the exhaust gas treatmentdevice flows through the supply opening into the cooling device. Theinlet and the supply opening are preferably provided in the immediatevicinity of the housing to produce an effective air flow through thecooling device.

The inlet is advantageously oriented in a travel direction of a vehiclein which the internal combustion engine is arranged since in this waythe relative wind can be made use of for producing the air flow.

In one example, provision is made for at least one inlet which widens inthe travel direction towards the open end. A plurality of inlets of anydesired shape may be distributed both over the periphery of the exhaustgas treatment device and over the longitudinal extent thereof. Forexample, it is possible to make provision for a plurality of inletsarranged one behind the other and each widening in the travel directiontowards the open end. Here, the shape of the inlets may be selected suchthat a swirling of the air in the cooling device is obtained, forexample by curved or obliquely extending walls, and that, where desired,outlets and subsequent inlets may be provided in approximately the sameplane. This allows new cold cooling air flows to be supplied at alltimes along the assembly made up of thermoelectric generators, so thatthe cooling device is, as it were, subdivided into individual coolingair ducts, and the cooling air is divided up into individual cooling airflows.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic longitudinal section taken through an exhaustgas treatment device according to a first embodiment of the invention;

FIG. 2 shows a schematic longitudinal section taken through an exhaustgas treatment device according to a second embodiment of the invention;

FIG. 3 shows a front view of the exhaust gas treatment device accordingto the invention as shown in FIG. 2;

FIG. 4 shows a top view of the exhaust gas treatment device according tothe invention as shown in FIG. 2;

FIG. 5 shows a schematic longitudinal section taken through an exhaustgas treatment device according to a third embodiment of the invention;

FIG. 6 shows a front view of the exhaust gas treatment device accordingto the invention as shown in FIG. 5;

FIG. 7 shows a schematic longitudinal section taken through an exhaustgas treatment device according to a fourth embodiment of the invention;

FIG. 8 shows a front view of the exhaust gas treatment device accordingto the invention as shown in FIG. 7;

FIG. 9 shows a top view of the exhaust gas treatment device according tothe invention as shown in FIG. 7;

FIG. 10 shows a schematic longitudinal section taken through an exhaustgas treatment device according to a fifth embodiment of the invention;

FIG. 11 shows a top view of the exhaust gas treatment device accordingto the invention as shown in FIG. 10;

FIG. 12 shows a front view of the exhaust gas treatment device accordingto the invention as shown in FIG. 10; and

FIG. 13 shows a cross-section XIII-XIII taken through the exhaust gastreatment device according to the invention as shown in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a first embodiment of an exhaust gas treatment device 10,in particular for an internal combustion engine of a vehicle, whichincludes a housing 12 having an entrance 14 and an exit 16. A poroussubstrate 20 is accommodated in the housing 12 and has an exhaust gas 18flowing through the substrate 20. The substrate 20 is arranged in theflow path from the entrance 14 to the exit 16. At least onethermoelectric generator 22 is provided on the housing 12.

The exhaust gas treatment device 10 is, for example, a catalyticconverter for a motor vehicle, a particulate filter for a motor vehicle,or a combination of a catalytic converter and a particulate filter.Preferably, the porous substrate used consists of a metal foam, a metalsponge and/or a metallic hollow sphere structure, and has an inner andan outer contour in the shape of a cone or a truncated cone.

Thermoelectric generators 22 utilize a difference in temperature betweentwo points of a conductor to generate an electrical voltage. Thestructure and function of such generators 22 are known from the priorart and will not be discussed in further detail. In each of the Figures,the thermoelectric generator 22 is applied to the outside of the housing12 and is illustrated merely schematically and greatly simplified.

Furthermore, an active cooling device 24 is provided which surrounds thethermoelectric generator 22 on the outside. The cooling device 24includes at least one cooling duct 26 through which a cooling medium 28flows. The cooling medium 28 is a liquid or, preferably, air.

The housing 12 has a largely cylindrical shape with an oval or polygonalbase. In one example, the housing has a hexagonally shaped base. Thethermoelectric generator 22 makes use of the temperature gradient thatdevelops in a radial direction between the housing 12 and the coolingdevice 24 to generate an electrical voltage. The greater the temperaturegradient between the housing 12 and the cooling device, the higher theelectrical voltage generated by the generator 22. In a preferredvariant, the hot exhaust gas 18 therefore flows directly against aninner side of the housing wall to reach as high a housing temperature aspossible. The heat is absorbed especially well if the housing 12 hasheat conducting fins 30 on the inside. Heat conducting fins 30 may alsobe provided on an outside of the housing 12 and/or on an inside of thegenerator 22 to achieve a particularly efficient heat transfer from thehousing 12 to the inside of the generator 22. In a similar fashion, thethermoelectric generator 22 may also be provided with heat conductingfins 30 on its outside, which protrude into the cooling duct 26 andensure a particularly efficient cooling of the outside of the generator22.

Provision may also be made for a plurality of cooling ducts 26 spacedapart in the peripheral direction.

Further embodiments of the exhaust gas treatment device 10 areillustrated in FIGS. 2 to 13. Since there are no differences from thefirst embodiment with regard to the design and functioning in principle,reference is made in this respect to the above description in relationto FIG. 1, and only the special features of these exemplary embodimentswill be discussed

FIG. 2 shows the exhaust gas treatment device 10 according to a secondembodiment, in which the cooling device 24 includes at least one inlet32 pointing in the travel direction and having a supply opening 34, sothat cooling medium 28, preferably air from the surroundings of theexhaust gas treatment device 10, flows through the supply opening 34into the cooling device 24. According to FIG. 2, the supply opening 34is made to be very large to allow a good air intake, with the inlet 32tapering inwardly towards the cooling duct 26. Since the inlet 32 ispositioned in the region of a conical housing neck 35, the inflowcross-section is extremely large.

FIGS. 3 and 4 show the exhaust gas treatment device according to FIG. 2in a front view and a top view, respectively. In this case, the housing12 is of a cylindrical design with a hexagonal base, with a flatthermoelectric generator 22 having heat conducting fins 30 beingfastened to each of the outer sides of the side surfaces of thecylinder.

FIGS. 5 and 6 show a longitudinal section and a front view,respectively, of the exhaust gas treatment device 10 according to athird embodiment, which differs from the second embodiment merely inthat the inlet 32 of the cooling device 24 on a later bottom surface ofthe exhaust gas treatment device 10 does not extend beyond the coolingduct 26 in the radial direction. The inlet 32 is not widened or is lesswidened in this region in order to enlarge the supply opening 34, but isflattened (cf. FIG. 6) so as to restrict as little as possible theground clearance of the vehicle in which the exhaust gas treatmentdevice 10 is installed.

FIG. 7 shows a fourth embodiment of the exhaust gas treatment device 10,in which the cooling device 24 includes a plurality of inlets 32arranged axially one behind the other in relation to a longitudinal axisA. The inlets 32 here are each formed such that they radially widen inthe travel direction towards the open end, i.e. towards the supplyopening. FIGS. 8 and 9 illustrate the associated front view and top viewof the exhaust gas treatment device 10.

FIGS. 10 to 12 show a longitudinal section, a top view, and a frontview, respectively, of the exhaust gas treatment device 10 in accordancewith a fifth embodiment, the cooling device of which likewise includes aplurality of inlets 32, 32′ arranged axially one behind the other inrelation to a longitudinal axis A. In this embodiment the thermoelectricgenerator 22 is however subdivided into two separate sections 36, 38,which are axially spaced apart from each other and are arranged onebehind the other. In relation to the flow direction of the coolingmedium 28, the cooling duct 26 has an undulating shape at the rear endof a front section 36.

At the front end of the rear section 38, the cooling duct 26 has a rearinlet 32′, which is likewise of an undulating shape. The front inlet 32is rotated in relation to the rear inlet 32′ in the peripheraldirection, so that a wave trough and a wave crest are always disposedaxially behind each other (cf. FIG. 12). This allows cooling medium thathas already been heated in the front section 36 to flow out of thecooling duct 26 into the surroundings between the sections 36, 38 of thethermoelectric generator 22 and “fresh” cooling medium from thesurroundings to flow into the cooling duct 26 at the same time to coolthe rear section 38 of the generator 22. Since the efficiency of thethermoelectric generator 22 would be very low in this inflow and outflowregion, the generator 22 is recessed in this region, so that the axiallyforward section 36 and the axially rearward section 38 are produced.

FIG. 13 shows a cross-section XIII-XIII through the exhaust gastreatment device according to FIG. 11, the section being taken betweenthe sections 36, 38 of the thermoelectric generator, and with theexhaust gas and cooling medium flows being indicated by arrows.

The exhaust gas 18 flows out radially through the substrate 20 at a highvelocity and impinges as a turbulent flow onto the housing 12, inparticular onto the fins 30 of the housing 12. Due to this turbulentflow, an especially good heat transfer is effected between the exhaustgas 18 and the housing 12.

With respect to the flow of the cooling medium 28, FIG. 13 againillustrates that cooling medium 28 that has already been heated in thefront section 36 of the generator 22 can escape from the cooling duct 26between the sections 36, 38 of the generator 22 (dashed arrows) and, atthe same time, fresh cooling medium 28 can flow into the cooling duct26.

In all of the embodiments, the hot exhaust gas flows directly againstthe inner side of the housing 12.

No elastic support mat for supporting the substrate is provided.

The substrate formed from the hollow metal spheres or the metal spongeis radially elastic and may also be directly clamped radially in thehousing.

Also, the substrate need not necessarily be a hollow body, but may asolid body.

According to the illustrated embodiments, the substrates are fastened toa linkage or a holding mechanism in a region of their axial ends, theholding mechanism, for its part, being fitted to the housing.

Although an embodiment of this invention has been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

1. An exhaust gas treatment device for an internal combustion engine,comprising: a housing including an entrance and an exit; at least oneporous substrate accommodated in said housing wherein an exhaust gasflows through said at least one porous substrate, and wherein said atleast one porous substrate is arranged in a flow path from said entranceto said exit; and at least one thermoelectric generator provided on saidhousing.
 2. The exhaust gas treatment device according to claim 1,wherein said at least one thermoelectric generator is applied on anoutside of said housing.
 3. The exhaust gas treatment device accordingto claim 1, wherein said exhaust gas flows against an inner wall of saidhousing.
 4. The exhaust gas treatment device according to claim 1,wherein said at least one porous substrate consists of at least one of ametal foam, metal sponge, and a metallic hollow sphere structure.
 5. Theexhaust gas treatment device according to claim 1, including heatconducting fins provided on at least one of an inside and an outside ofsaid exhaust gas treatment device.
 6. The exhaust gas treatment deviceaccording to claim 1, including a cooling device for said thermoelectricgenerator.
 7. The exhaust gas treatment device according to claim 6,wherein said cooling device surrounds an outside of said thermoelectricgenerator.
 8. The exhaust gas treatment device according to claim 6,wherein said cooling device includes at least one cooling duct having acooling medium flowing through said at least one cooling duct.
 9. Theexhaust gas treatment device according to claim 8, wherein said coolingmedium is air.
 10. The exhaust gas treatment device according to claim9, wherein said cooling device includes at least one inlet having asupply opening so that air from surroundings of said exhaust gastreatment device flows through said supply opening into said coolingdevice.
 11. The exhaust gas treatment device according to claim 10,wherein said at least one inlet widens in a vehicle driving directiontowards an open end.
 12. The exhaust gas treatment device according toclaim 11, wherein said at least one inlet comprises a plurality ofinlets arranged one behind each other, said plurality of inlets wideningin the vehicle driving direction towards said open end.